Coupled Palladium–Tungsten Bimetallic Nanosheets/TiO₂ Hybrids with Enhanced Catalytic Activity and Stability for the Oxidative Removal of Benzene

Abstract

Since the conventional Pd-based catalysts often suffer severe deactivation by water, development of a catalyst with good activity and moisture-resistance ability is of importance in effectively controlling emissions of volatile organic compounds (VOCs). Herein, we report the efficient synthesis of ultrathin palladium–tungsten bimetallic nanosheets with exceptionally high dispersion of tungsten species. The supported catalyst (TiO2/PdW) shows good performance for benzene oxidation, and 90% conversion is achieved at a temperature of 200 °C and a space velocity of 40 000 mL g–1 h–1. The TiO2/PdW catalyst also exhibits better water-tolerant ability than the traditional Pd/TiO2 catalyst. The high catalytic efficiency can be explained by the facile redox cycle of the active Pd2+/Pd0 couple in the close-contact PdO x –WO x –TiO2 arrangement. We propose that the reason for good tolerance to water is that the lattice oxygen of the TiO2/PdW catalyst can effectively replenish the oxygen in active PdO x sites consumed by benzene oxidation. A four-step benzene transformation mechanism promoted by the catalyst is proposed. The present work provides a useful idea for the rational design of efficient bimetallic catalysts for the removal of VOCs under the high humidity conditions.

Advances in Catalytic Oxidation of Volatile Organic Compounds over Pd-Supported Catalysts: Recent Trends and Challenges

“…The bimetallic Pd-Ce/γ-Al 2 O 3 catalyst displayed better catalytic performance than Pd/γ-Al 2 O 3 , further indicating that Ce loading improved the catalytic activity by reducing the amount of precious metals incorporated within the catalyst (Ren et al, 2020). The high water-resistant ability of the supported Pd−W bimetallic catalysts was ascribed to the presence of the facile redox cycle of the active Pd 2+ /Pd 0 couple (Liang et al, 2019). The addition of Mo in Pd/Al 2 O 3 catalyst efficiently improved the activity and stability by increasing the Pd dispersion and changing the partial PdO (He et al, 2014).…”

“…It was proposed that the overall catalytic oxidation reaction included three steps: 1) adsorption of propane over the S-1 shell and reaction with lattice oxygen from cerium oxide to form enolate or acetone species; 2) decomposition of enolate or acetone species and subsequent formation of bicarbonate and formate species by lattice oxygen; and 3) further oxidation of bicarbonate and formate species into H 2 O and CO 2 , which underwent refilling of the lattice of cerium oxide by the gaseous oxygen. The benzene oxidation pathway over TiO 2 /PdW-S was proposed by Liang et al (Liang et al, 2019) (Figure 1). It was proposed that benzene was initially oxidized by the surface oxygen to form phenolate species, followed by the transformation of phenolate species into the benzoquinone (e.g., o-benzoquinone and p-benzoquinone) species.…”

“…The L-H mechanism emphasizes the surface reaction between the adsorbed molecules on analogous active sites, and the surface reaction between the adsorbed reactant and molecules from the gas phase was included in the E-R mechanism (Kamal et al, 2016). Among them, the MVK kinetic model is usually adapted to elucidate the VOC oxidation process over Pd-supported catalysts (He et al, 2010a;He et al, 2010b;Jablonska et al, 2015;Liang et al, 2019). However, unlike the conventional Pd-based catalysts in which the MVK mechanism governs the oxidation of VOCs, the catalytic oxidation of toluene over Pd supported on mesoporous activated carbons followed the L-H mechanism (Bedia et al, 2010).…”

Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review

“…In particular, platinum group metal (PGM) catalysts are often used as state-of-the-art catalysts to remove various contaminants. 167–172 The photocatalytic gaseous reaction occurs at the outermost layers of the metal atoms. Still, the inner layer of the active metal or metal oxides never interacts with the gaseous reactant molecules.…”

Single-atom site catalysts for environmental catalysis

“…The environment catalysis can be defined as the study of catalysts and catalytic reaction impacting the environment [9]. Supported metal catalysts, especially supported platinummetal-group (PGM) catalysts, are commonly utilized as the state-of-the-art catalysts to eliminate gaseous pollutants [10][11][12][13][14][15]. However, only the outermost layer of metal atoms is often involved in the catalytic process but active atoms inside metal or metal oxides are never reached by gas molecules, thereby considered as wasted [16].…”